CN1374069A - Magnetic resonance imaging apparatus and its magnetic field change measuring method and compensating-method - Google Patents

Magnetic resonance imaging apparatus and its magnetic field change measuring method and compensating-method Download PDF

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CN1374069A
CN1374069A CN01137484A CN01137484A CN1374069A CN 1374069 A CN1374069 A CN 1374069A CN 01137484 A CN01137484 A CN 01137484A CN 01137484 A CN01137484 A CN 01137484A CN 1374069 A CN1374069 A CN 1374069A
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后藤隆男
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GE Medical Systems Global Technology Co LLC
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    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
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    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
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    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56563—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/443—Assessment of an electric or a magnetic field, e.g. spatial mapping, determination of a B0 drift or dosimetry

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Abstract

For the purpose of compensating for a variation in the static magnetic field of an MRI apparatus, RF probes 1P1 and 1P2 are placed and a reference static magnetic field is measured as a reference frequency in the beginning; the static magnetic field is measured at an appropriate time as a frequency to determine the amount of static magnetic field variation from their difference; and the transmission frequency of an RF pulse and the receiving detection frequency of an NMR signal are corrected or the gradient current for a gradient coil is corrected so as to compensate for the amount of the magnetic field variation.

Description

MR imaging apparatus and changes of magnetic field measuring method and compensation method
Background of invention
The present invention relates to be used for changes of magnetic field measuring method and the changes of magnetic field compensation method and the MRI device of MRI (nuclear magnetic resonance) device, more particularly, the changes of magnetic field measuring method that relates to the static magnetic field that is used to measure the MRI device, the changes of magnetic field compensation method of the static magnetic field of MRI device, and the MRI device that can realize such method.
The static magnetic field of MRI device should be constant, but when metallic object (for example automobile), during near MRI device or environment change (for example, variations in temperature), static magnetic field may produce undesirable variation.
Before, the measure of handling this variation of static magnetic field concentrates on the cause that suppresses to change, for example by carrying out air-conditioning with the magnetic shield of MRI device or to the room that the MRI device is installed.
Yet, even the variation of static magnetic field still takes place after taking these measures sometimes, in this case, the undesirably problem of deterioration of picture quality quilt appears.
Abstract of invention
Therefore first purpose of the present invention provides a kind of changes of magnetic field measuring method of variation of the static magnetic field that can measure the MRI device.
In addition, second purpose of the present invention provides a kind of changes of magnetic field compensation method of variation of the static magnetic field that can compensate the MRI device.
In addition, the 3rd purpose of the present invention provides the MRI device that can suitably realize changes of magnetic field measuring method and changes of magnetic field compensation method.
The changes of magnetic field measuring method that provides according to a first aspect of the invention, it is characterized in that: near configuration I (wherein I 〉=1) RF (radio frequency) probe image-region of MRI device, each probe have the little phantom circuit that can launch FID (non-inductive decay) signal and the combination of small coil; When witness mark magnetic field, send the RF pulse and receive the FID signal so that determine reference frequency f from described FID signal from described RF probe Ir(wherein i=1-I); When measuring changes of magnetic field, send the RF pulse and receive the FID signal so that determine frequency f from described FID signal from described RF probe iAnd determine j rank changes of magnetic field α by finding the solution following equation j: f i - f ir = Σ j = 0 I - 1 α j · r i j , The position r of each RF probe wherein iExpression.
In the changes of magnetic field measuring method of described first aspect, at when beginning configuration RF probe and with the form witness mark static magnetic field of reference frequency, and measure static magnetic field at reasonable time with the form of frequency, so that determine the static magnetic field variable quantity from their difference.If the RF probe is fixed, then can determine (I-1) changes of magnetic field at most usually.
The changes of magnetic field measuring method of the aforementioned arrangements that provides according to a second aspect of the invention is characterized in that I=2, and definite zeroth order changes of magnetic field α 0With single order changes of magnetic field α 1
In the changes of magnetic field measuring method of second aspect, the RF probe is fixed, can determine zeroth order and single order changes of magnetic field.
The zeroth order changes of magnetic field is the changes of magnetic field with location independent, and the single order changes of magnetic field is the linear function of position.
The changes of magnetic field measuring method that provides according to a third aspect of the invention we is characterized in that: across 2 RF probes of the image-region of MRI device configuration, each probe has the little phantom circuit that can send FID (non-inductive decay) signal and the combination of small coil; When witness mark magnetic field, send the RF pulse and receive the FID signal so that determine reference frequency f from described FID signal from described RF probe 1rAnd f 2rWhen measuring changes of magnetic field, send the RF pulse and receive the FID signal so that determine frequency f from described FID signal from described RF probe 1And f 2And determine zeroth order changes of magnetic field α by finding the solution following equation 0With single order changes of magnetic field α 1: α 0 = ( f 1 - f 1 r ) + ( f 2 - f 2 r ) 2 α 1 = ( f 1 - f 1 r ) - ( f 2 - f 2 r ) 2
In the changes of magnetic field measuring method of the third aspect, the RF probe is fixed, can determine zeroth order and single order changes of magnetic field.
The changes of magnetic field measuring method of the aforementioned arrangements that provides according to a forth aspect of the invention, it is characterized in that: being pressed for time of witness mark magnetic field is connected on before the pulse train that is used for first image imaging begins, and is connected on and is used for second and before the pulse train of image imaging subsequently begins and measure being pressed for time of changes of magnetic field.
In the changes of magnetic field measuring method of fourth aspect, when repeating imaging pulse sequence so that collect when filling the spatial data of k-, before each imaging pulse sequence begins, measure changes of magnetic field, therefore can handle the variation in magnetic field during near the MRI device when metallic object.
The object lesson of imaging pulse sequence comprises the pulse train of observing gtadient echo, such as pulse train according to GRASS (gradient is rechecked and gathered under the stable state) or SPGR (incomplete GRASS).
The changes of magnetic field measuring method of the aforementioned arrangements that provides according to a fifth aspect of the invention, it is characterized in that: the time in witness mark magnetic field is the time that the MRI device starts, and the time of measuring changes of magnetic field is the regular time interlude of being separated by after the MRI device starts.
In the changes of magnetic field measuring method aspect the 5th, because the regular time measurement changes of magnetic field at interval time of being separated by when the MRI device starts and after starting, so when environmental change, can handle changes of magnetic field.
The changes of magnetic field measuring method of the aforementioned arrangements that provides according to a sixth aspect of the invention is characterized in that: the MRI device is the MRI device of open type, and this device produces static magnetic field in vertical direction, the RF probe configuration on imaging region and below.
In the changes of magnetic field measuring method aspect the 6th, the static magnetic field that can suitably measure Open MR I device changes, and wherein the homogeneity in magnetic field realizes by the machinery adjustment or by increasing a plurality of fritter magnets or ferrum.
The changes of magnetic field penalty method that provides according to a seventh aspect of the invention is characterized in that, according to the zeroth order changes of magnetic field α that measures by the changes of magnetic field measuring method of aforementioned arrangements 0, proofread and correct the transmission frequency of RF pulse and the reception detection frequency of nuclear magnetic resonance, NMR (NMR) signal.
In the changes of magnetic field penalty method aspect the 7th, the zeroth order static magnetic field changes and can compensate by the transmission frequency of correction RF pulse and the reception detection frequency of NMR signal.
The changes of magnetic field penalty method that provides according to an eighth aspect of the invention is characterized in that, single order of measuring according to the changes of magnetic field measuring method by aforementioned arrangements and high-order changes of magnetic field α more jCome the correction gradient electric current.
In the changes of magnetic field penalty method of eight aspect, single order and more the electromagnetostatic field of high-order change and can compensate by the correction gradient electric current.
The MRI device that provides according to a ninth aspect of the invention is characterized in that comprising: I (wherein I 〉=1) RF probe, and each probe is configured near the imaging region by launching the little phantom circuit of FID signal and constituting of small coil; The reference frequency deriving means is used for sending the RF pulse from described RF probe when wanting witness mark magnetic field, and receives the FID signal so that determine reference frequency f from described FID signal Ir(wherein i=1-I); The frequency deriving means is used for sending the RF pulse from described RF probe in the time will measuring changes of magnetic field, and receives the FID signal so that determine frequency f from described FID signal iAnd the changes of magnetic field accountant, be used for determining j rank changes of magnetic field by finding the solution following equation: f i - f ir = Σ j = 0 I - 1 α j · r i j , Wherein the location tables of each RF probe is shown r i
In the MRI device aspect the 9th, can suitably realize the changes of magnetic field measuring method of first aspect.
The MRI device of the aforementioned arrangements that provides according to the tenth aspect of the invention is characterized in that I=2, and has determined zeroth order changes of magnetic field α 0With single order changes of magnetic field α 1
Can suitably realize the changes of magnetic field measuring method of second aspect in the MRI device aspect the tenth.
The MRI device that provides according to an eleventh aspect of the invention is characterized in that comprising: two RF probes, and each probe is configured near the imaging region by launching the little phantom circuit of FID signal and constituting of small coil; The reference frequency deriving means is used for sending the RF pulse from described RF probe in the time will measuring changes of magnetic field, and receives the FID signal so that determine reference frequency f from described FID signal 1rAnd f 2rThe frequency deriving means is used for sending the RF pulse from described RF probe in the time will measuring changes of magnetic field, and receives the FID signal so that determine frequency f from described FID signal 1And f 2And the changes of magnetic field accountant, be used for determining zeroth order changes of magnetic field α by finding the solution following equation 0With single order changes of magnetic field α 1: α 0 = ( f 1 - f 1 r ) + ( f 2 - f 2 r ) 2 α 1 = ( f 1 - f 1 r ) - ( f 2 - f 2 r ) 2
In the MRI device of the tenth one side, can suitably realize the changes of magnetic field measuring method of the 3rd aspect.
The MRI device of the aforementioned arrangements that provides according to a twelfth aspect of the invention, it is characterized in that being pressed for time of witness mark magnetic field is connected on before the pulse train that is used for first image imaging begins, measure being pressed for time of changes of magnetic field and be connected on and be used for second and before the pulse train of image imaging subsequently begins.
In the MRI device aspect the 12, can suitably realize the changes of magnetic field measuring method of the 4th aspect.
The MRI device of the aforementioned arrangements that provides according to a thirteenth aspect of the invention, the time that it is characterized in that witness mark magnetic field is MRI device start-up time, and the time of measuring changes of magnetic field is the regular time interlude of being separated by after the MRI device starts.
In the MRI device aspect the 13, can suitably realize the changes of magnetic field measuring method of the 5th aspect.
The MRI device of the aforementioned arrangements that provides according to a fourteenth aspect of the invention is characterized in that the MRI device is the MRI device of open type, and this device produces static magnetic field in vertical direction, the RF probe configuration on imaging region and below.
In the MRI device aspect the 14, can suitably realize the changes of magnetic field measuring method of the 6th aspect.
The MRI device of the aforementioned arrangements that provides according to a fifteenth aspect of the invention is characterized in that comprising the RF frequency correcting apparatus, is used for according to the zeroth order changes of magnetic field α that measures 0Proofread and correct the transmission frequency of RF pulse and the reception of NMR signal and detect frequency.
In the MRI device aspect the 15, can suitably realize the changes of magnetic field penalty method of the 7th aspect.
The MRI device of the aforementioned arrangements that provides according to a sixteenth aspect of the invention is characterized in that comprising the gradient current correcting unit, is used for according to the single order of measuring and the changes of magnetic field α of high-order more jCome the correction gradient electric current.
In the MRI device aspect the 16, can suitably realize the changes of magnetic field penalty method of the 8th aspect.
According to the changes of magnetic field measuring method of MRI device of the present invention, can measure by variable quantity near the metallic object (for example automobile) of MRI device or environment change (for example temperature change) or the like caused static magnetic field.
In addition, the changes of magnetic field penalty method according to MRI device of the present invention can compensate the variation of the static magnetic field of MRI device.
And, according to MRI device of the present invention, can suitably realize changes of magnetic field measuring method and changes of magnetic field penalty method.
To understand further aim of the present invention and advantage more according to detailed description to the most preferred embodiment of the present invention of graphic extension in the accompanying drawing.
Description of drawings
Fig. 1 is the cutaway view of the major part of graphic extension MRI device according to an embodiment of the invention.
Fig. 2 is the cutaway view of graphic extension according to an example of RF probe of the present invention.
Fig. 3 is the configuration block diagram that shows MRI device according to an embodiment of the invention.
Fig. 4 is the block diagram that shows according to the example of NMR signal transmission/receiving circuit of the present invention.
Fig. 5 is the flow chart that shows according to the operation of changes of magnetic field compensation method of the present invention.
Detailed description of the present invention
Below the embodiments of the invention shown in the accompanying drawing will be described in more detail.Be noted that the present invention is not limited to these embodiment.
Fig. 1 is the cutaway view of the major part of graphic extension MRI device 100 according to an embodiment of the invention.
MRI device 100 is Open MR I devices, and this device is by the permanent magnet 1M1 and the 1M2 of configuration produce static magnetic field in vertical direction relatively up and down.
On permanent magnet 1M1 and 1M2 surface, dispose magnetic adjustable plate Sp respectively, be used for to hold therein the inner imaging region that produces static magnetic field of receiving coil IR of object with homogeneous.
Permanent magnet 1M1 and 1M2, magnetic adjustable plate Sp, and base deflection coil By and magnetic pole deflection coil Py formation magnetic circuit.
Configuration gradient coil 1G separately is used to produce gradient magnetic on the surface of each magnetic adjustable plate Sp.
At gradient coil 1G internal configurations transmitting coil 1T, be used to send the RF pulse, the latter is in order to the nuclear spin of excitation interior of articles.
Receiving coil 1R is used to receive the coil that rises from the NMR of object signal.
In addition, above a RF probe 1P1 was installed in, below the 2nd RF probe 1P2 was installed in, they inserted between gradient coil 1G and the transmitting coil 1T.
Be noted that and use superconducting magnet to replace permanent magnet 1M1 and 1M2.
Fig. 2 is the cutaway view of graphic extension RF probe 1P1 and 1P2.
RF probe 1P1 and 1P2 respectively have such configuration, wherein, and NaCl solution or CuSO are housed 4The little phantom circuit Ft that can launch the FID signal of solution and combine around the small coil Co of little phantom circuit Ft.
Fig. 3 is the configuration block diagram that shows MRI device 100.
In MRI device 100, magnet assembly 1 comprises permanent magnet 1M1 and 1M2, receiving coil 1R, gradient coil 1G, transmitting coil 1T and RF probe 1P1 and 1P2.
Receiving coil 1R is connected to preamplifier 5.
Gradient coil 1G is connected to gradient coil exciting circuit 3.
Transmitting coil 1T is connected to RF power amplifier 4.
RF probe 1P1 and 1P2 are connected to NMR signal transmission/receiving circuit 15.
Sequence memory circuit 8 response from the instruction of computer 7 according to imaging pulse sequence, for example according to imaging pulse sequence, the operation gradient coil excitation circuitry 3 of spin echo technique, thereby produce X-axis gradient magnetic, Y-axis gradient magnetic and Z axial gradient magnetic field by gradient coil 1G.(each gradient coil 1G is made up of X-axis gradient coil, Y-axis gradient coil and Z axis gradient coil.) sequence memory circuit 8 goes back actuating doors modulation circuit 9, has the predetermined timing and the pulse signal of envelope shape so that will be modulated into from the high frequency output signal of RF oscillating circuit 10.This pulse signal is added to RF power amplifier 4 as the RF pulse signal, carries out power amplification in RF power amplifier 4, is added to the transmitting coil 1T in the magnet assembly then so that send the RF pulse from transmitting coil IT.
Preamplifier 5 amplify by receiving coil 1R from object detection to the NMI signal, and signal imported phase discriminator 12.Phase discriminator 12 is used to from the output signal of RF oscillating circuit 10 as receiving detection signal, the NMR signal from preamplifier 5 is carried out phase-detection, and the signal after this phase-detection is offered analog-digital converter 11.Analog-digital converter 11 becomes digital signal MR data with this phase detection analog signal conversion, and is entered into computer 7.
7 pairs of these MR data of computer are carried out visual reconstructed operation, so that produce the MR image.The MR pictorial display is in display device 6.Computer 7 also is responsible for comprehensive control example as receiving the information input from bench board 13.
In addition, computer 7 is carried out the field compensation processing procedure.Specifically, it is via digital processing circuit 16 operation NMR signal transmission/receiving circuits 15, so that will arrive little phantom circuit Ft from the RF pulsing of the small coil Co in the RF probe 1P1, and receive the FID signal of phantom circuit Ft from childhood at small coil Co place, then according to the FID signal determine the changes of magnetic field amount with the gradient current of the frequency of oscillation of proofreading and correct RF oscillating circuit 10 or correction gradient coil 1G so that the compensating field variable quantity.This field compensation method will be explained in more detail with reference to figure 5.
Fig. 4 shows the configuration block diagram of the example of NMR signal transmission/receiving circuit according to an embodiment of the invention.
NMR signal transmission/receiving circuit 15 comprises RF exciting circuit 150, door modulation circuit and the RF power amplifier that comprises the RF oscillating circuit; Multiplexer 151 is used to switch the output destination from the RF pulsing signal of RF exciting circuit 150 outputs; Transmission/reception change-over switch 152 and 153 is used for switching to the transmission of the RF pulsing signal of RF probe 1P1 and 1P2 with between the reception of the FID received signal of RF probe 1P1 and 1P2; Preamplifier 154 and 155 is used to amplify the FID received signal from RF probe 1P1 and 1P2; Adder 156 is used for the FID received signal additions in preamplifier 154 and 155 amplifications; Low-converter 157 is used for the frequency inverted of FID received signal is arrived intermediate frequency range; And intermediate frequency amplifier 158, be used to amplify the FID signal frequency that becomes intermediate frequency range.
Digital processing circuit 16 responses become the FID conversion of signals numerical data and are input to computer 7 from the instruction operation NMR signal transmission/receiving circuit 15 of computer 7.
Fig. 5 shows by MRI device 100 to carry out the flow chart that field compensation is handled operation.Be right after in the pulse train that is used for first image imaging and begin or before MR device 100 starts, start field compensation method (when for example starting in the morning).
Among the step ST1, the RF pulse sends and obtains FID signal N from the RF probe IrFor example, the RF pulse sends and receives FID signal N from a RF probe 1P1 Ir
At step ST2, according to FID signal N IrI and Q determine phase IrAnd ask phase (t), Ir(t) to the differential of time t so that determine reference frequency f IrFor example, according to FID signal N IrDetermine reference frequency f Ir
At step ST3, if do not obtain the reference frequency of all RF probes, then this processing procedure is returned step ST1; Otherwise transfer to step ST4.For example, if only obtain the reference frequency f of a RF probe 1P1 Ir, then processing procedure is returned step ST1 so that obtain the reference frequency of the 2nd RF probe at step ST1 and ST2, and processing procedure is transferred to step ST4 then.
At step ST4, processing procedure is waited until the variation that measures magnetic field, and when measuring changes of magnetic field, processing procedure is transferred to step ST5.The time of measuring changes of magnetic field be right after be used for second and the beginning of the pulse train of image imaging later on before or the regular time interval that after MRI device 100 starts, is separated by () time for example, per hour.
At step ST5, the RF pulse sends and obtains ID signal N from the RF probe iFor example, the RF pulse sends and receives FID signal N from a RF probe 1P1 1
At step ST6, according to FID signal N iI and Q determine phase IrAnd ask phase (t), Ir(t) to the differential of t so that determine reference frequency f iFor example, according to FID signal N 1Determine frequency f 1
At step ST7, if do not obtain the frequency of all RF probes, then this processing procedure is returned step ST5, otherwise transfers to step ST8.For example, if only obtain the frequency f of a RF probe 1P1 1, then processing procedure is returned step ST5 so that obtain the frequency f of the 2nd RF probe 1P2 at step ST5 and ST6 2, processing procedure is transferred to step ST8 then.
At step ST8, determine j rank changes of magnetic field α by finding the solution following equation j: f i - f ir = Σ j = 0 I - 1 α j · r i j , Wherein the location tables of each RF probe is shown r i
For example, when at its zero (0,0,) be positioned at the quadrature coordinate system (x at imaging region center, y, z) in, the coordinates table of first RF probe is shown (0,0, r) and the coordinates table of the 2nd RF probe 1P2 be shown (0,0 ,-r), and I=2 then determines zeroth order changes of magnetic field α by finding the solution following simultaneous equations 0With single order changes of magnetic field α 1:
f 1-f 1r＝α 0+α 1·r
f 2-f 2r＝α 0-α 1·r
That is to say, determine zeroth order changes of magnetic field α by the expression that changes aforesaid equation 0With single order changes of magnetic field α 1As follows: α 0 = ( f 1 - f 1 r ) + ( f 2 - f 2 r ) 2 α 1 = ( f 1 - f 1 r ) - ( f 2 - f 2 r ) 2
At step ST9, according to zeroth order changes of magnetic field α 0Proofread and correct the frequency of oscillation of RF oscillating circuit 10.
At step ST10, according to single order and high-order changes of magnetic field α 1... the gradient current of correction gradient coil 1G, for example, according to single order changes of magnetic field α 1Offset current on the Z axis gradient coil ...The gradient delta G that is corrected is: ΔG = α 1 2 r · γ , Wherein γ represents gyromagnetic ratio.
If on three or three above positions, fix three or three above RF probes or move the RF probe so that obtain the FID signal, then can compensate second order or high-order changes of magnetic field more three or three above positions.
Then, this processing procedure turns back to step ST4.
Many far different embodiments of the invention of possible configuration within the spirit and scope of the present invention.Know that very the present invention is not limited to the specific embodiment that description is described, except the content of appended claims definition.
Symbol
(Fig. 1)
The 100MRI device
1M1, the 1M2 permanent magnet
Sp magnetic adjustable plate
The 1G gradient coil
1P1,1P2 RF probe
The 1T transmitting coil
The 1R receiving coil
By base deflection coil
Py magnetic pole deflection coil
(Fig. 2)
1P1,1P2 RF probe
The Co small coil
The little phantom circuit of Ft
(Fig. 3)
100 MRI devices
1 magnet assembly
The 1G gradient coil
The 1T transmitting coil
1M1, the 1M2 permanent magnet
The 1R receiving coil
1P1 RF probe
1P2 RF probe
3 gradient coil exciting circuits
4 RF power amplifiers
5 preamplifiers
15 NMR signal transmission/receiving circuits
9 modulation circuits
10 RF oscillating circuits
12 phase discriminators
8 sequence memory circuits
11 A/D converters
16 digital processing circuits
6 display devices
13 operating board
7 computers (Fig. 4)
152 transmission/reception change-over switches
153 transmission/reception change-over switches
151 MUX
154 preamplifiers
155 preamplifiers
150 RF exciting circuits
157 low-converters
158 IF amplifiers (Fig. 5)
Start field compensation operation ST1 from a RF probe transmitting RF pulse and reception FID signal N IrST2 is according to FID signal N IrI and Q determine phase Ir(t), and
Ask phase Ir(t) to the differential of time t so that determine reference frequency f IrDoes ST3 obtain the reference frequency of all RF probes? has ST4 arrived the time of measuring changes of magnetic field? ST5 is from a RF probe transmitting RF pulse and receive FID signal N iST6 is according to FID signal N iI and Q determine phase i(t), and
Ask phase i(t) to the differential of time t so that determine frequency f iDoes ST7 obtain the reference frequency of all RF probes? ST8 determines α by finding the solution following equation j: f i - f ir = Σ j = 0 I - 1 α j · r i j , ST9 is according to α 0The frequency of oscillation ST10 that proofreaies and correct the RF oscillating circuit is according to α jProofread and correct j rank changes of magnetic field

Claims (16)

1. changes of magnetic field measuring method said method comprising the steps of:
Near configuration I (wherein I 〉=1) the RF probe image-region of MRI device, each probe have the little phantom circuit that can launch FID (non-inductive decay) signal and the combination of small coil;
When witness mark magnetic field, send the RF pulse and receive the FID signal so that determine reference frequency f from described FID signal from described RF probe Ir(wherein i=1-I);
When measuring changes of magnetic field, send the RF pulse and receive the FID signal so that determine frequency f from described FID signal from described RF probe iAnd
Determine j rank changes of magnetic field α by finding the solution following equation j: f i - f ir = Σ j = 0 I - 1 α j · r i j , The position r of each RF probe wherein iExpression.
2. the changes of magnetic field measuring method of claim 1 is characterized in that: I=2, and definite zeroth order changes of magnetic field α 0With single order changes of magnetic field α 1
3. changes of magnetic field measuring method said method comprising the steps of:
Across 2 RF probes of the image-region of MPI device configuration, each probe has the little phantom circuit that can launch FID (non-inductive decline) signal and the combination of small coil;
When witness mark magnetic field, send the RF pulse and receive the FID signal so that determine reference frequency f from described FID signal from described RF probe 1rAnd f 2r
When measuring changes of magnetic field, send the RF pulse and receive the FID signal so that determine frequency f from described FID signal 1And f 2And
Determine zeroth order changes of magnetic field α by finding the solution following equation 0With single order changes of magnetic field α 1: α 0 = ( f 1 - f 1 r ) + ( f 2 - f 2 r ) 2 α 1 = ( f 1 - f 1 r ) - ( f 2 - f 2 r ) 2
4. claim 1 or 3 changes of magnetic field measuring method, it is characterized in that: measure and describedly be connected on before the pulse train that is used for first image imaging begins, be connected on and be used for second and before the pulse train of image imaging subsequently begins and measure being pressed for time of changes of magnetic field with reference to being pressed for time of magnetic field.
5. claim 1 or 3 changes of magnetic field measuring method, it is characterized in that: measure described time and be described MRI device and start constantly, and the time of measuring described changes of magnetic field is the regular time interlude of being separated by after described MRI device starts with reference to magnetic field.
6. claim 1 or 3 changes of magnetic field measuring method is characterized in that: the MRI device that described MRI device is an open type, this device produces static magnetic field in vertical direction, and described RF probe configuration on described imaging region and below.
7. a changes of magnetic field penalty method said method comprising the steps of: according to the described zeroth order changes of magnetic field α by measuring according to the described changes of magnetic field measuring method of claim 1 or 3 0Proofread and correct the transmission frequency of RF pulse and the described reception detection frequency of NMR signal.
8. changes of magnetic field penalty method said method comprising the steps of: according to by the described single order measured according to the described changes of magnetic field measuring method of claim 1 or 3 and more the high-order changes of magnetic field come the correction gradient electric current.
9. MRI device, it comprises:
I (wherein I 〉=1) RF probe, each probe is configured near the imaging region by launching the little phantom circuit of FID signal and constituting of small coil;
The reference frequency deriving means is used for sending the RF pulse and receiving the FID signal so that determine reference frequency f from described FID signal from described RF probe when wanting witness mark magnetic field Ir(wherein i=1-I);
The frequency deriving means is used for sending the RF pulse and receiving the FID signal so that determine frequency f from described FID signal from described RF probe in the time will measuring changes of magnetic field iAnd
The changes of magnetic field accountant is used for determining j rank changes of magnetic field by finding the solution following equation: f i - f ir = Σ j = 0 I - 1 α j · r i j , Wherein the described location tables of each RF probe is shown r i
10. the MRI device of claim 9 is characterized in that: I=2, and definite zeroth order changes of magnetic field α 0With single order changes of magnetic field α 1
11. a MRI device, it comprises:
Two RF probes, each probe is configured near the imaging region by launching the little phantom circuit of FID signal and constituting of small coil;
The reference frequency deriving means is used for sending the RF pulse and receiving the FID signal so that determine reference frequency f from described FID signal from described RF probe when wanting witness mark magnetic field 1rAnd f 2r
The frequency deriving means is used for sending the RF pulse and receiving the FID signal so that determine frequency f from described FID signal from described RF probe in the time will measuring changes of magnetic field 1And f 2And
The changes of magnetic field accountant is used for determining zeroth order changes of magnetic field α by finding the solution following equation 0With single order changes of magnetic field α 1: α 0 = ( f 1 - f 1 r ) + ( f 2 - f 2 r ) 2 α 1 = ( f 1 - f 1 r ) - ( f 2 - f 2 r ) 2
12. the MRI device of claim 9 or 11, it is characterized in that: measure and describedly be connected on before the pulse train that is used for first image imaging begins, be connected on and be used for second and before the pulse train of image imaging subsequently begins and measure being pressed for time of described changes of magnetic field with reference to being pressed for time of magnetic field.
13. the MRI device of claim 9 or 11 is characterized in that: measure described time and be the time that described MRI device starts, and the time of measuring described changes of magnetic field is the regular time interlude of being separated by after described MRI device starts with reference to magnetic field.
14. the MRI device of claim 9 or 11 is characterized in that: the MRI device that described MRI device is an open type, this device produces static magnetic field in vertical direction, and described RF probe configuration on described imaging region and below.
15. the MRI device of claim 9 or 11 is characterized in that also comprising the RF frequency correcting apparatus, is used for the zeroth order changes of magnetic field α according to described measurement 0Proofread and correct the transmission frequency of RF pulse and the reception of NMR signal and detect frequency.
16. the MPI device of claim 9 or 11 is characterized in that also comprising the gradient current correcting unit, is used for according to the single order of described measurement and the changes of magnetic field α of high-order more jCome the correction gradient electric current.
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Family Cites Families (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4284950A (en) * 1978-08-05 1981-08-18 E M I Limited Imaging systems
US4685468A (en) * 1983-03-18 1987-08-11 Albert Macovski NMR imaging system using field compensation
US4623844A (en) * 1983-07-18 1986-11-18 Albert Macovski NMR inhomogeneity compensation system
JPS6267433A (en) * 1985-09-20 1987-03-27 Yokogawa Electric Corp Nmr imaging apparatus
US4950994A (en) * 1988-03-07 1990-08-21 General Electric Company Gradient and polarizing field compensation
US4885542A (en) * 1988-04-14 1989-12-05 The Regents Of The University Of California MRI compensated for spurious NMR frequency/phase shifts caused by spurious changes in magnetic fields during NMR data measurement processes
US4970457A (en) * 1989-04-05 1990-11-13 The Regents Of The University Of California MRI compensated for spurious rapid variations in static magnetic field during a single MRI sequence
EP0538668B1 (en) * 1991-10-25 1996-06-26 The University Of Queensland Correction of signal distortion in an NMR apparatus
DE19508238A1 (en) * 1995-03-08 1996-09-12 Siemens Ag Magnetic field stabilisation method for NMR device
DE19536390A1 (en) * 1995-09-29 1997-04-03 Siemens Ag Fundamental field measurement appts. for controlling fundamental field of NMR tomography magnet
US5905377A (en) * 1996-07-31 1999-05-18 Board Of Trustees Of The Leland Stanford Junior University Method and apparatus for correcting gradient system and static magnetic field in magnetic resonance imaging

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